Physics

Electromagnetic Waves and Spectrum

670 Questions

Electromagnetic waves and spectrum questions test a candidate's understanding of radiation frequencies, wavelengths, and the properties of different rays like infrared, ultraviolet, and visible light. Concepts also cover practical applications in astronomy and the fundamental speed of light calculations. This physics topic appears regularly in general science sections of major competitive examinations.

UV rays propertiesElectromagnetic radiation frequencyWavelength identificationSpeed of light calculationsBlack body radiation

Electromagnetic Waves and Spectrum Questions

Multiple choice physics spectra the electromagnetic spectrum electromagnetic spectrum electromagnetic waves

Name the radiations of wavelength just longer than $8\times 10^{-7}m$.

  1. infrared

  2. ultrared

  3. infraviolet

  4. ultraviolet
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

In the order of increasing wavelength, the waves are Gamma rays ($< 1 nm$), X-rays ($1-10 nm$), infrared rays ($700-{ 10 }^{ 5 }nm$), micro waves (${ 10 }^{ 5 }-{ 10 }^{ 8 }nm$), radio waves (${ >10 }^{ 8 }nm$).
Hence, the radiations of wavelength just longer than ${ 8\times 10 }^{ -7 }m$ is Infrared.

Multiple choice physics spectra the electromagnetic spectrum electromagnetic spectrum electromagnetic waves

Fraunhofer spectral lines are called:

  1. Line absorption spectra

  2. Line emission spectra

  3. continuous spectra

  4. Continuous emission spectra
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Fraunhofer spectral lines are also called line absorption spectra. They are a set of spectral lines. The lines were originally observed as dark features (absorption lines) in the optical spectrum of the Sun.

Multiple choice physics spectra the electromagnetic spectrum electromagnetic spectrum electromagnetic waves

Electromagnetic waves of wavelength ranging from $100\mathring{A}$ to $\mathring{A}$ comes under 

  1. X-rays

  2. UV regions

  3. Visible region

  4. Infrared region
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation
X-rays: $10 nm-10 pm\  i.e.\ 10^{-8}m-10^{-11}m$
Given frequency range: $100 \mathring A-  1 \mathring A\ i.e.\ 10^{-8}m-10^{-10}m$
Hence, given wavelength range falls under X-rays
Multiple choice physics spectra the electromagnetic spectrum electromagnetic spectrum electromagnetic waves

According to the electromagnetic spectrum, radio waves have the ___frequency and the  _______ wavelength.

  1. lowest; largest

  2. lowest; smallest

  3. highest; smallest

  4. highest; largest

  5. medium; medium
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Radio waves are the least energetic waves among other waves. They have the lowest frequency and thus the largest wavelength. Due to this large wavelength character, the radio waves are used in data transmission purposes, since they are hard to interact with particles in the atmosphere.

Multiple choice physics spectra the electromagnetic spectrum electromagnetic spectrum electromagnetic waves

According to the electromagnetic spectrum, As the frequencies of the pure spectral colours increase, the wavelengths of the colours:

  1. decrease

  2. increase

  3. remain the same

  4. decrease by a factor of 2

  5. increase by a factor of 2
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Speed of all the electromagnetic waves is constant and is equal to speed of light  i.e  $c$

Using        $\lambda \times \nu = c = constant$
$\implies$ If frequencies of the pure spectral colours increase then their wavelength will decrease.

Multiple choice physics spectra the electromagnetic spectrum electromagnetic spectrum electromagnetic waves

If a particular electromagnetic wave has the highest frequencies among the other electromagnetic waves then it should have the smallest

  1. wavelengths

  2. speeds

  3. amplitudes

  4. energies

  5. periods
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Electromagnetic waves travel with constant speed equal to that of light  i.e  $v =c= constant$

For EM waves       $\lambda \times \nu = c =$ constant
Thus waves with highest frequency will have smallest wavelength.

Multiple choice physics spectra the electromagnetic spectrum electromagnetic spectrum electromagnetic waves

Find out the wavelength of violet light which has a frequency of $7.5 \times 10^{14}Hz$ ?

  1. $2.25\times 10^{23}m$
  2. $2.5\times 10^{5}m$
  3. $4\times 10^{-7}m$
  4. $7.5\times 10^{-7}m$
  5. $2.25\times 10^{7}m$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Given :    $\nu = 7.5 \times 10^{14}$  Hz

Speed of violet light (EM wave)     $v = 3 \times 10^8$ m/s
Thus wavelength of violet light         $\lambda = \dfrac{v}{\nu}  = \dfrac{3 \times 10^8}{7.5 \times 10^{14}}  =4 \times 10^{-7}$ m